Method of and apparatus for obtaining optical effects by electrical means



Feb. 4, 1936 w WALTQN 2,029,401

& METHOD OF AND APPARATUS FOR OBTAINING OPTICAL EFFECTS BY ELECTRICAL MEANS Filed Jan. 14, 1932 5 Sheets-Sheet l m m mmmmm m Fe. 4, .1936. A G. w. WAL'IA'ON ,0 9,40

METHOD OF AND APPARATUS FOR OBTAINING OPTICAL EFFECTS BY ELECTRICAL MEANS Filed Jan. 14, 1952 A '5 Sheets-Sheet 2 Feb. 4; 1936. WAL+ N 2,029,401

METHOD OF AND'APPARATUS FOR OBTAINING OPTICAL EFFECTS BY ELECTRICAL MEANS Filed Jan. 14, 1952 5 Sheets-Sheet 5 Feb; 4, 1936. G w WALTON v 2,029,401

METHOD OF AND APPARATUS FOR OBTAINING OPTICAL EFFECTS BY ELECTRICAL MEANS 5 Sheets-Sheet 4 Feb. 4, 1936. wCw 2,029,401

METHOD OF AND APPARATUS FOR OBTAINING OPTICAL EFFECTS BY ELECTRICAL MEANS Filed Jan. 14, 1932 5 Sheets-Sheet 5 Patented Feb. .4, 1 936 uu'iraos'rnrss PATENT OFFICE METHOD OF AND APPARATUS FOR OBTAIN ING OPTICAL EFFECTS BY ELECTRICAL MEANS George William Walton, London, England Application January 14, 1932, Serial No. 588,684 In Great Britain January 19, 1931 16 Claims.

mechanical apparatus, such as oscillating mirrors with apertures and the like, by electrical gas discharge tubes such as neon-lamps, and by using the Faraday or Kerrefl'ects with plane polarized light, all of which have inherent disadvantages. For instance, the mechanical devices and the electric gas discharge tube are not sufficiently rapid in their response, and the Faraday and Kerr eflects require the use of polarizing prisms, which besides being costly, are usually of'very small aperture so that the light which canbe passed is very limited, and moreover considerable heating takes place in the control devices themselves,more particularly in the Kerr cells, which renders the performance irregular.

,- The invention is based on the following properties of a refracting medium. Every gaseous, liquid, or solid medium'through which light passes. has a'particular refractive index, and when a ray of light passes from one medium to another medium of a different refractive index,

the ray of light is deflected from its original path when it strikes the boundary surface at an angle; other than 90. The deflection follows the law, that the sine of the angle the emergent ray makes with the normal at the boundary surface, at the point of emergence, is equal to the sine of the angle the incident ray makes with that normal, multiplied by the refractive index, when passing from a medium of a higher to one of a lower index, and divided by the refractive index, when passing from a medium of a lower into another of a higher index. Every medium has a particular speed of light propagation through it, and this speedis proportional to the reciprocal of the refractive ,index. It is therefore, possible toregard refrac- T tionpurely fromrthe point of view ofthe proparespect to the sines of the incident and emergent angla. Again, the refractive index of a medium has a, definite relation to the dielectric properties {of that medium, the specific inductive capacity of a transparent dielectric being equal to the square of the refractive index.

The refractive index of a vacuum is 1, and it has been found that it is modified when there is an electric discharge in the vacuum. It has also 5 been found that the refractive index of any dielectric is modified when submitted to electrical influences.

The properties above referred to are made use of in the present invention. 1 The invention will now be described, by way of example with reference to the accompanying diagrammatic drawings; in which:

Fig. 1 shows one form of vacuum device according to the invention,

Fig. 2 being a section thereof along the plane 2 -2 in Fig. 1 and Fig. 3 being an explanatory diagram. 3 Figs. 4, 5, and

6 show modifications of Fig. 1,

Fig. 'i showsa further modification of Fig. 1, 20 Figs. 8 and 9 show the applicationof the invention to the control of light intensity.

Fig. 10 shows a modified form of device pro- Fig. 13 being an explanatory diagram,

Fig. 14 shows a type of device for obtaining combined prism and lens effects,

Fig. 15 being an explanatory diagram thereof.

' Fig. 16 shows a type of device according to the invention in which use is made of a'solid medium,

Figs. 17 and 18 Fig. 19 shows a further modification of Fig. 16

being modifications thereof.

in which use is made of electrolite or colloid re sisters.

Fig. 20 shows a modification in which use made of a fluid medium.

Fig. 21 shows a. sistant film is used.

Figs. 22 and 23 ing arrangements,

Figs. 25, 26, 27,

' Fig. 24 being an explanatory diagram of Fig.

device in which only one re show modifications of' reflect- 45 and 28 show arrangements in 1' which a source of light is provided outside the vessel of an electric discharge device. Fig. 29 illustrateaa device in which also of photoelectric emission,

Figs. 30 and31, 32, 33, and

use is made a and I j 34 illustrate different modifications in which use is also made of a control electrode. i I

Referring to Figs. 1, 2, and 3,1, is the envelope of a vacuum tube,

2 is a pinch in which the leads 4, 1, and III are sealed to the supports 3, 5, and 9 respectively, the latter being also mounted in the pinch. The support 3 supports the filament 5 which is preferably rendered brightly incandescent, as the device is used also as a source of illumination, the other end of the filament 5 being connected to the support 6. The filament 5 is surrounded by an open-ended cylinder 8 of transparent insulating material, such as glass, whichis supported by the support 9 serving also as a connection, as well as by the support I I. On the interior surface of the cylinder 8 there is deposited a high resistance-conducting film I5 which is semi-transparent, for instance such as sputtered platinum, the connection therewith being effected by1 means of the support 9 which is in the form of a cop.

The battery I3.suppl'ies current to the filament 5 through the leads 4 and I. The resistant film I5 on the cylinder 8 is connected to the battery I 4 through the loop support 9 and lead Ill, a positive potential being applied thereto relatively to the filament 5. As'the film I5 constitutes an anode with respect to the filament .5, electrons will be drawn towards it from the filament, the velocity, and the number of the electrons being dependent on the positive potential of the, film. Whena thermionic current is flowing through the device there is a potential drop in the film I5 between the two side portions of the loop 9, which, if. the film-is of even thickness and resistance, is such that at a point midway between the sides of the loop 9, the potential relative to the filament 5 is lowest, and gradually increases towards both sides of the loop 9 where it is highest.

- The anode thus comprises a high resistant film with a relatively highly conducting region on the edges of the film. I

In Fig. 3 which shows only the filament 5, the resistant film I5 and loop 9, light from the filament 5, when there is no potential on the film/I5, will arrive at all points on I5 simultaneously if the centre of curvature of I5 is at 5. When a potential is applied to the film I5, owing to the potential drop along it, light will arrive at the centre point I6 thereof at a different time than at points 9, since the electrical influence causes the speed of light along 5-I6 to be difierent from that along 5--9. The refractive index and therefore the speed of.light propagation depends on the intensity of the electrical influence; conse quently there is a change of wavefront of the light from 5, which, if there is-an advance along 59 ascompared with the path along 5-I6, is such that the apparent position of 5 is changed to 5:1, and the new wavefront is 9aI69a.

If the device described isincluded in a normal optical system, say to produce an image of the fllament,. it will behave as a cylindrical lens of varying focal length controlled by electrical influence without movement of any parts, and may therefore be used with great advantage for many different purposes."

In Fig. 4, which shows a modification of the device illustrated in Fig. 1, the resistant film I5 is fiat instead of cylindrical. Fig. 5 illustrates a modification in which the anode film I5 between the connecting leads 9 is convex with respect to the filament 5, its centre of curvature being at I 1. Fig. 6 shows a modification in which the centre of curvature of the concave film I5 lies at Ill between the film and the filament. Generally the n "is arrangement of Figr2 is themost convenient one,

although in special cases the other shapes may be of advantage. In choosing the best shape for a particular purpose, the distance of a point of IS from the filament 5 must be taken into consideration together with the potential of that point tre and greatest at the edges, near the loop 9.

The filament 5 is concentrated to approximately a point source of light, though this is not essential.

Many other forms, elliptical and otherwise, may be used to obtain special optical effects and the film I5 mayobe curved cylindrically, spherically or spheroidally, by suitably shaping the support 8.

One of the principal uses of the invention is as a light control device, and a typical arrangement for this purpose is shown in Fig. 8. In this figure, 5 is the incandescent filament, which serves as the source 'of light as well as for the operation of the device as described above, and I5 is the highly resistant film. I8 is a normal lens, which, when no potential is applied to I5, will focus an image of the filament 5 at the point 20, the apertured member having the slit I9 however reducing the amount of light at 20 to a very low value. When potential is applied to I5 relatively to 5, the apparent or virtual image of 5 is shifted to 5a and consequently, with the application of sufiicient potential, the lens I8 forms an light from 5 passes through the slit. As the potential on I5. is reduced, the light passing through the slit is also reduced to a minimum as above referred to.

Fig. 9 shows a negatively acting arrangement in which an increase in potential reduces the light passing through the slit. An opaque stop 2i placed at the focus 20, at which the light passing through the slit I9 is a minimum, prevents any light from passing if it is of the same size as the image of 5 at .20. As the potential on the film I5 is decreased, the light passing through the slit I9 is increased. A stop may be placed in the same way at 20 in Fig. 8, so that the minimum light shall be zero.

Fig. 10 shows a type of device in which the effect produced is reversed as compared with the effect produced by the arrangement of Fig. 1. For this purpose a single contact 9 is provided in the centre .of the high resistant film I5. Fig. 11, which is similar to Fig. 3, shows the reversed action which is produced. The wavefront of the tively to that indicated in Fig. 3. The construction according to Fig. 10 may be used in the arrangements according to Figs. 8 and 9, in each case the relation between --thelight passing through the slit and the applied potential being reversed to those shown in Figs. 8 and 9.

In a'similar manner a reversal of the effect produced by the apparatus of Fig v 7 may be effectedby arranging the highlyconducting region 9 of the modest the centre of theresistant film' lowest potential relatively to the filament 5. Fig.

13 shows the effect obtained, viz. how "the general tr'avelling direction oflight is changed.

when a potential is applied to the contact 9 and therefore to the film l5, there 1S 8- drop of potential across the latter, which causes the speed of light along 5-9 to be different from that along 5-16. This results in a change of wavefront to 90- 18, so that the virtual image of 5 is at 51;, i. e. displaced sideways, which corresponds to the efiect of a prism.

shown in Figs 8 and 9, an image of the filament 5 being focussed on to the slit 19, which image will be displaced sideways when a potential is applied to the film l5 relatively to the filament 5. Combined prism and cylindrical lens effects may"be obtained by an arrangement as shown in Fig; 14. The one edge of the film i5 is connected to the connector 9 and the other edge to the connector 22,- the two connectors being connected together through a resistor 23 of smaller resistance than the film l5 "between' the connectors 9 and 22, so that the potentials applied to the two edges are different. In consequence thereof there is some point on l5 where the potential is lowest. Fig. 15' shows the double displacement of the virtual image 5a ofthe filament 5 Similar but reversed lens effects may be obtained with the device described with reference to 'Fig. 10 if the connector 9 is not in the centre of the film l5. I

Effects similar to those above described may be obtained by using gaseous liquid and transparent or translucent solid mediums.

Fig. 16 shows. an arrangement in which the medium consists of a solid dielectric-30 on the surface of which are deposited the high resistant films l5 and'l5a. The connection with l5 is.

effected by connectors 24 and 25 and with l5'a by connectors 25 and 21. A battery 28'is connected to 24 and 26 and another battery 29 to 25 and 21, in such a manner that 24 and 21 are positive and 25 and 26 negative, whereby a current a is caused to pass through the resistant films l5 The construction according to Fig. 12 may also be used in the arrangements battery as, the edges of the films being connected by the connectors 3| and 32. This device produces efiects similar to those obtained with the construction according to Fig. 10.

The device shown in Fig. 18 produces a prism effect such as obtained with the device according to 12 and effects such as obtained'by the I device according to Fig. 14 may be obtained by an arrangement such as shown in Fig. 16, if one battery is of lower voltage than the other,-or by 25 are not central and one end connection has appreciable resistance.

The high resistant semi-transparent films may be replaced by transparent conducting liquids, colloids, and the like by using a suitable cell atrangement such as is shown in Fig. 19, wherein the cell 32, which is entirely of transparent ma} a construction such as shown in Fig. 1'7, if 24 and terial, such as glass, has a member 30 dividing it 'into two compartments filled with a liquid, such as water, connections being made, as in Fig. 17,

with the liquid films l5 and i511.

, In all these devices use may be made of a vary-v ing potential such as alternating current from a source 28, television signals and the like.

Generally solid mediums are so rigid that differences of strain in them, to produce the effects above described, can only be obtained when the thickness isvery small as compared with the length; as shown in Figs. 16 to 19. Gases, prefer ably under pressure, and liquids are moresatisfactory and a suitable type of. device using a liquid medium is shown in Fig. 20. The cell 39 is provided with the films l5 anda on its parallel inner surfaces, connection being made with them by means of connectors 24 and 25 respectively, and otherwise as shown in Fig. 1'7. The cell contains a transparent liquid dielectric, such as oil or the like. When gas is used the device must of course be sealed. Other efiects such as those obtained by the devices shown in Figs. 1, 10,12, and 14 may be obtained with devices similar to that of Fig. 20 by using suitable connections and potentials as described in connection with Figs.

16, 1'7, and 18. In all the Figs. 16-20, use is made of two re-' 'sistant-films l5 and i5a to produce the difierences of electricalinfiuence in the medium between them, but this is not essential. Fig- 21 shows a device having only one resistant film l5, and a conductor 34 having very little or no voltage drop across it. By connecting 34 to reversed efiects are obtained as compared with those obtained when, asshown in Fig. 21, 34 is and I la and a potential drop to be produced along them. As a result thereof, at the point IS, the potential difference between 15 and I5a is zero, if the batteries are of equal voltage and the resistances of the films l5 and l5a vary in the same regular manner across the surfaces of 39 and the potential difference at the edgesis greatest, so that the refractive index of is least at the edges and greatest at the centre. In consequence thereof light is more retarded in the centre and a cylindrical lens effect is produced when light passes through the thickness of 30. The plate 30 may be of lenticular shape and only one source. of I potentialneed be used if 24 and 21 and similarly I V 25 and 25 are connected together. The effect obtained with this device is similar to that obtained with the construction shown in Fig. 1.

Fig. 17 shows a similar device havinga reversed" effect. The connection with the films l5 and 15a is made at 24 and 25 from the two poles of the connected to 24. Prism effects may be'obtained -:by having no connectionbetween the source of potential and 34- and by applying the potential between the connectors'25 and 26 and connecting 34 to one of them. Combined prism and lens effects may be obtained by using the arrangement of Fig. 21 with a resistor connected in the lead to 25 or 26. The conductor 34'may of course be transparent such as a fluid or colloid, or it may be an opaque metallic film, light passing,

through 30 on to it and being reflected back through I9, but the effects will be similar, though increased, owing to the double passage through 39.

cylindrical, spherical or spheroidal curvature, as desired. Such an arrangement is shown in Fig.

22,-. in which 35is a source of light,an image of which would be focused by the mirror, at'il, if

when the device according to Fig. 21 is pro-- vided with a reflecting surface, it may be shaped to form a convex or concavemlrror having a no potential were applied. However, when a potential 'is applied, the image is formed at some other point 31a, which is on the same optical cording to a modification,

axis, if the device has a plain lens effect and extra-axial, if the device has a prism eflect.

All the devices shown in Figs. 16 to 20. may be used with arefiector to obtain an increased effect, by causing light to pass twice through them. The devices shown in Figs. 1, 4, 7f 10, 12, and 14 may also be made reflecting, either directly from the high resistant film l5, or-by providing a suitable reflecting surface as shown in Fig. 23.

e In Fig. 23 the support 8 for the resistant film least further removed'from l5 than is 5.

- In the vacuum devices hereinbefore described,

the source of light was mounted within them, but this is not essential as it rate. Such an arrangement is shown in-Figs. 25 and 26. An external source of light 35. is focussed by means of a lens 39 on to or near. the filament 5. The latter is of the dull emitting type and is bi-filar, as shown,

ture necessary to obtain electric emission, more particularly if 35 is an arc-lamp or-an equivalent powerful light; alternatively the filament may be heated in the usual way. Fig. 26 shows the gem eral arrangement and the paths of light: Ac-

light from the source 35 may pass through 8 and I5,before it is 1'0- cussed on 5. The filament 5 need not be bi-filar; on the other hand it may be more distributed, e. g.

as shown in Figs. 27 and 2 8. The lighti'rom 85- is not focussed as in Figs. 25 and26, the effect obtained being much the same as in the case of the construction according to Fig. 16.

,fictually the filament is not sufliciently'distributed in Fig. 27 but this may beovercome by arranging a screen 40 as shown in Fig. 28, such as a fine wire mesh and the like, to which a positive constant potential is applied relatively to the filament, whereby a more even distribution of the electrons from 5 to i5 is ensured.

In a further, type of vacuum device, the efl'ects hereinbe tore described are obtained by making use 01" photo-electricemission. Such a device is shown in Fig. 29, in which the highly resistant film i5 is of a material which is photo-electrically active.

v 01' light passing through Under the' influence the device, the film V which are collected by the anode 4|, the latter being preferably in. the form of a .wire mesh or the like, and the connection therewith being .made by means of a lead 42. A positive potential eflects above described.

is applied to the anode 4| relatively to the film II, the variations of which The anode 4| may be concentrated in a single wire, a small circle or even the point of a wire, according to the particu-.

lar effect which it is desired to secure. The 'vacuum devices hereinbetore: described have not been provided with control electrodes, butsuch electrodes may thermionicdevices. Figs. 35 and 81 show such a type, in-which a control member in the-tom of a grid is interposed'between the filament I in Fig.- 24. When a r 5, the apmay be entirely sepathe heat or the light from 35 heating the filament unto the temperaemits electrons potential produce. the

be. used, as in ordinary *beso shaped'es and the'resistant film I5 which constitutes the anode. The connection with the grid 43 ismade by means or alead 44. In this case a constant positive potential is applied to the film l5 rela- 5 tively to the filament. 5;, and a varying potential, such as television signals and the like, may be applied between 43 and 5. The voltage drop across the'film i5 depends on the thermionic current, which in its turn depends on the. potential 1 of 43 relatively to 5, so that the optical etlect of the device varies with the grid potential. In Fig. 31. which shows a section of the" device and the circuits connected to it, M is a source of constant potential to be applied to the film l5, and 15 28 are the terminals to which is connected the source of varying potential to be applied to the grid 43.

The control member maybe any of the types used in known thermionic devices. For instance, 20 it may take the form of the screen 40 shown in Fig. 28, so that in that device there would bee. secondfine. wire mesh between 40 may be on that side of the filamentwhich is furthest away from the anode It. The varying 25 potential may be appliedbetween the control member and the high resistant film, i. e. in Fig. 31, the terminals 28 would be connected to the 'leads l9 and 44 respectively, instead of as shown ,in'that figure. I a 30 The high resistant film itself may also be the control member. This is shown in Fig. 32, 45 being the anode which is in the form 01' a screen ofwires, and the resistant film l5 influencing the electrons which pass from the filament B to the 35 anode 45, although-the film lfilsnotin the path. The operating varying potential is applied between the filament 5 and the film l5." Alternatively, the film l5 may have a centre connector ll as well as two' side .connectors-O, as shown in Fig. 33, and the varying potential he applied between .41 and 9, as shown. In this case the action 01' the film I5 is similar to that in Fig. 21.

The film may be applied outsideof the vessel I, e. g. deposited on its external surface as shown 5 in Fig. 34, or on the opposite side, i. e. nearest to the filament 5, but in such a case it is prererabl'e' that the filament be distributed as shown in Figs. 27 and28, and in Fig. 32.

The resistant film I! of the devices hereinbetore described need not be of uniform resistance. In fact in some cases, when itis uneven, it attold; a very ready means 01' correction of defects, peculiar to the device itself, as wellas for optical aberrations oi the normal type. For instance,

when the device shown in Fig. 1 has a film of even resistance, it has'a' peculiart aberration, since it 'acts as twoprisms, base to base, the point I in Fig. 3 beingthe junction of the bases: consequently the wave front in that figure would not so be exactly cylindrical, but each half Il -9a. would have natural curvature; the two halves being reversed relatively to each other. The amount 01' deviation from true cylindricalform is very small in practice,' but it can be completely coro5 rectedrif the resistant film varies in thickness, and therefore in resistance, from II to 9. This variation can be j 'readily obtained during the formation or the film by sputtering. Similarly,

in all other cases the'film may be varied in thickness in order to obtaina desirable modification of the optical efl'e'ct of the device. In the case oi liquid or colloidal resistors asin Fig. 19, the

' compartment containing such" a resistor would to obtain the desired variation v and IE, or it h of resistance, and consequently the desired potential at different parts of the resistor.

Most of the above devices have been described as giving cylindrical lens efiects, but all of them 5 may be constructed to give a spherical lens efiect, by suitably arranging the resistant film con-' nections and the other electrodes associated therewith, for instance as described in'connection with Fig. 7. v It is to be understood that the invention is not f limited to the examples hereinbefore given and that the details for carrying it into eflect may be modified in various respects without in any way departing from the spirit of the invention. WhatI claim as new and desire 'to secure by Letters Patent of the United statesis: r

l. The'method of producing a refractive eiiect upon light with the aid of an electrically stressed light transmitting medium disposed in the path of said light which comprises establishing in the Q direction of said path, an electrostatic stress having at least a component which is constant at -any one point but differs from one point to another in a direction transverse to said path and passing a beam of light through said medium along said path. i g

2. The method oi producing electrically the effect of a lens, with the aid of an electrically influenced light transmitting region disposed in a light path; which comprises establishing in said region an; electrostatic influence which changes in magnitude progressively and in the same sense from the centre-oi said region to the boundaries thereof in a direction transversely of said path and passinga beam of light through said region along said path.

3. The methodof producing electrically the efiect of a lens, with the aid of an electrically stressed transparent region disposed in a light 4 path, which comprises establishing in said region, in the direction oisaid path, an electrostatic stress the magnitude of which changes progressively, and in the same sense, from the centre of said region to the boundaries thereof in a direction transverse of said path and passing a beam of lightthrough said region along said path.

4. The method of producing electrically the effect of a prism with the aid of an electrically stressed transparent, region disposed in a light path, which comprises establishing in said region, in the direction of said path, an electrostatic stress the magnitude of which changes progressively from one boundary of said region to another in a direction transverse oi. said path and passing: a beam oi light through said region alongsaid path. 5. Electro-optical apparatus comprising an electrode in the form of an electrically resistive film, a second electrode. a light transmitting me- 00 dium between said electrodes, a relatively'highly conducting region on said film, means for applying a potential difierence between said second electrode and said highly conductive region, and means providing an electrical conducting path 5 1 independent of said highly conducting region between said second electrode and said resistive film whereby the potential difi'erence between said second'electrode and said highly conductive region can be madesubstantially diflerent from the potential difference between said second electrode and points on said resistive film.

6. Apparatus according to claim 5, wherein said film is adapted for the passage of light therethrough. r 3 '1. Electro-optical apparatus comprising an 'stantially centrally thereof, means, for applying a electrode in the form of an electrically resistive film, a second electrode, a light transmitting medium between said electrodes, a relatively highly conducting zone extending across said film subent of said highly conducting zone between said second electrode and said resistive film whereby 10 the potential difference between said second electrode and said highly conductive zone can be made substantiallyv different from the potential difference between said second electrode and points on said resistive film. 15

8. llllectro-optical apparatus comprising. an electrode in the form of an electrically conducting but resistive film, a second electrode, a light transmitting region between said electrodes, a relatively highly conducting'zone extending sub- 20 stantially around said film, terminal means for applying a potential diileren'cebetween said second electrode and said highly conducting zone, and means permitting a iiow or current between said electrodes in response to a potential difier- 25 ence applied between said terminakmeans.

9. Electro-optical apparatus comprising an electrode in the form of an electrically conducting but resistive film, a second electrode, a light transmitting 'medium between said electrodes, a 30 relatively ,highly conducting zone extending across said film upon a part of one side thereof, terminal means for'applying a potential differ- -ence between said se ond electrode and said highly conducting zone, and means permitting 35 a. flow of current between said electrodes in response to a potential diiierence applied between said terminal means.

-10. An electric discharge .device adapted to produce a refractive optical effect upon light and 40 comprising within an evacuated envelope a cathode capable of being heated to an electron emitting temperature, an anode adapted for the passage of light therethrough and having a region of relatively high conductivity and a region of 5 relatively low conductivity, a light transmitting path betweensaid anode and said cathode, and terminals outside said envelope connected to said cathode and said relatively highly conducting region.

11. An electric discharge device according to claimlO, wherein there is provided a third electrode positioned to control the intensity ofthe electron stream between said anode and cathode:

12. The method of producing a varying re- 55 fractive optical effect upon light with the aid of an electrically stressed light transmitting medium disposed in the path of said light, which comprises establishing in said medium, an 6180? trostatic field, the intensity of which is difierent '00 at dififerent parts of said medium in a direction transversely oisaid path, producing a variation of the intensity of the electrostatic field at all points of the electrostatic field simultaneously and passing a beam of light along said path. 05

13. The method of producing a refractive optical effect upon light withthe aid of an electrically influenced light transmitting region disposed in the-path of said light, which comprises establishing in said region an electrostatic field, 70 the intensity oi-which has at least a component which is constant, at anyone point but different at difierent parts of said region in a. direction duce a refractive optical efiect, said apparatus comprising an evacuated envelope containing two electrodes and a light transmitting medlium be- :1, resistive region a relatively highly conductivere 'gi'on whereby a smoothly progressive change of I Lpotential can be established over said highly resistive region in response to a steady potential difference applied between said electrodes.

15. The method of varying the intensity of a beam of light in accordance with changes in electrical potential difference which comprises causing said beamto pass first through a transparent region which is subjected to electrical stress, the intensity of which differs from one point to another in a direction transverse of said path and thenthrough an apertured member,

and changing the potential difference to produce a change in the average intensity of said electrical stress, and thereby to vary in accordance with said potential difference the fraction 01'' said beam which passes through said apertured member. I

16. A method of producing a refractive optical effect upon light with the aid of alight transmitting medium and two electrodes for establishing an electric stress insaid medium, one of said electrodes having a substantial electrical resistance in at least one direction, said method comprising the steps of passing light through said medium in' a direction transverse of the firstnamed direction, applying an electrical potential difierence between said electrodes to produce an I electrostatic field having a component in the direction of said light and causing a current to flow in said first-named direction through the electrode having substantial resistance to produce a substantial potential gradient along this electrode in said first-named direction.

GEORGE WALTON. 

